Corrosion protection for buried metallic objects

ABSTRACT

PROCESS FOR INHIBITING ELECTRICAL CORROSION BY INCREASING THE ELECTRICAL RESISTANCE OF THE SOIL SURROUNDING A METALLIC OBJECT BY ADDITION OF WATER-DISPLACING HIGH RESISTANCE MICELLAR DISPERSIONS TO THE SURROUNDING SOIL. THE MICELLAR DISPERSION IS COMPRISED OF SURFACTANT, AQUEOUS MEDIUM, HYDROCARBON, AND OPTIONALLY COSURFACTANT AND OR ELECTROLYTE.

Aug. 29, 1972 w, GQGARTY ETAL 3,687,609

CORROSION PROTECTION FOR BURIED METALLIC OBJECTS Filed Nov. 4, 1969 CONDUCTIVITY I,OOO

50 PERCENT WATER ATTORNEY nitecl States Patent 3,687,609 Patented Aug. 29, 1972 3,687,609 CORROSION PROTECTION FOR BURIED METALLIC OBJECTS William B. Gogarty, Littleton, (3010., and William P.

Bush, Findlay, Ohio, assiguors to Marathon Oil Company, Findlay, Ohio Filed Nov. 4 ,1969, Ser. No. 873,863 Int. Cl. C23f 11/00 U.S. Cl. 212.5 12 Claims ABSTRACT OF THE DISCLOSURE Process for inhibiting electrical corrosion by increasing the electrical resistance of the soil surrounding a metallic object by addition of Water-displacing high resistance micellar dispersions to the surrounding soil. The micellar dispersion is comprised of surfactant, aqueous medium, hydrocarbon, and optionally cosurfactant and/ or electrolyte.

BACKGROUND OF THE INVENTION Field of the invention This invention is concerned with the protection of metallic objects which are in contact with corrosive soil by the use of water-displacing, low conductivity micellar dispersions. It has been found that the addition of these micellar dispersions to the soil in contact with a buried or partially buried metallic object serves effectively to reduce corrosion due to the conductivity between the metallic object and the soil.

Although the addition of such micellar dispersions does give a completely independent source of corrosion protection, it is to be noted also that the addition of these compounds to the soil surrounding buried metallic objects which are under cathodic protection will enable the current density of the cathodic protection system to be considerably reduced. Micellar dispersions will also help to inhibit corrosion in systems protected by so-called sacrificial anodes. The method, therefore, also permits considerable savings in the costs of various other corrosion inhibiting techniques.

Corrosion problems are particularly acute when metallic objects such as pipelines, storage tank bottoms and fluid delivery and disposal systems, are in constant contact with soil, especially soil containing water. It is generally believed that corrosion is caused by electrochemical interaction of metals or alloys with their non-metallic environment. Since metals and alloys are electronic conductors and are built up of cations and electrons that are more or less easily dissociable, and since many environments, such as moisture laden soil, contain or produce in contact with the metal lattice, ionically conducting species, most corrosions are caused by electrochemical currents flowing between metallic objects and non-metallic surroundings and conducted largely by the moisture between these two materials. Therefore the introduction of an insulating waterdisplacing micellar dispersion between the metallic object and the surrounding soil will effectively insulate said metallic object from the electrochemical currents which are responsible for the corrosion process.

Conventional methods of protecting buried metallic objects such as pipelines include coating the metals with various compositions to prevent access of the corrosive medium, cathodic protection systems, and sacrificial anodeusually magnesium rods-protection systems. The prior art has also tried to inhibit corrosive effects by the introduction of other types of low conductivity compounds into the soil surrounding buried metallic objects. Examples of this method of inhibiting corrosion can be found in US. Pat. 3,192,720 wherein such low-conductivity compounds are prepared from soluble salts of copper and nickel with soluble ferroand ferri-cyanides. The main advantage of this invention is that micellar dispersions not only provide a low conductivity medium around the metallic object, but also effectively displace Waterthe material largely responsible for conducting the corrosion causing electrical currents.

SUMMARY OF THE INVENTION This invention provides a means whereby the corrosion of a metallic object such as a pipeline or storage tank may be reduced by impregnating the soil surrounding the metallic object with a low conductivity micellar dispersion which inhibits corrosion causing electrochemical currents. The process of this invention provides the soil with a water-displacing micellar dispersion comprised of surfactant, aqueous medium, hydrocarbon, and optionally cosurfactant and/or electrolyte. Since soils with low resistance are the result of high water saturation, displacement of the water by a material of low conductivity will increase the resistance of the soil. Micellar dispersions have a low conductivity and they also tend to displace the water in the soil. Furthermore, the conductivity of the micellar dispersions remains low even with water concentrations up to about 70%.

The term micellar dispersion as used herein is meant to include micellar solutions, micro-emulsions [Schulman and Montague, Annals of the New York Academy of Sciences, 92, pages 366371 (1961)], transparent emulsions (Blair, Jr., et al., U.S. Pat. No. 2,356,205) and micellar dispersion technology taught by C. G. Sumner, Claytons, The Theory of Emulsions and Their Technical Treatment, 5th edition, pages 315-320 (1954). Examples of useful micellar dispersions include those taught in US. Pats. Nos. 3,254,714; 3,275,075; 3,301,325; 3,307,628. The micellar dispersion can be oil-external or water-external. Preferably however, the micellar dispersions of this invention are the oil-external type since they are characterized by a higher electrical resistivity.

The micellar dispersion is comprised of hydrocarbon, aqueous medium phase, and at least one surfactant. One or more co-surfactants (also identified as cosolvents, cosolubilizers, and semi-polar organic compounds) are useful in the dispersions. Electrolytes may also be useful in producing these micellar dispersions. Also, the micellar dispersion can contain other additives, e.g. corrosion and scale inhibitors, such as polyalkylene amine salts of organic acids and polyamides of a long-chain fatty acid, oxidation inhibitors such as ditertiarybutyl-para-cresol and phenyl alphanaphthyl amine. Examples of useful dispersions include those containing, by volume, from about 4% to about hydrocarbon; from about 5 to about water, at least about 4% surfactant, from about 0.01 to about 20% or more by volume of cosurfactant and from about 0.001 or less up to about 5% or more by weight of electrolyte in the aqueous phase.

Examples of useful hydrocarbons include crude oil (both sweet and sour), partially refined fractions thereof, e.g. side cuts from crude columns, crude column overheads, gas oils, kerosene, heavy naphthas, naphthas, straight-run gasoline, and liquefied petroleum gases, refined fractions of crude oil and halogenated hydrocarbons. Pure hydrocarbons are also useful, e.g. paraflinic compounds including liquefied petroleum gases, propane, pentane, heptane decane, dodecane, etc.; cycloparafiin compounds including cyclohexane, etc.; aryl compounds including benzene, naphthalene, anthracene, etc.; alkylated products thereof including toluene, alkyl phenols, etc. and combinations of the hydrocarbons taught herein. Based on economics, the preferred hydrocarbon is one locally available and is crude oil. The unsulfonated hydrocarbon (e.g. heavy vacuum gas oils) in petroleum sulfonates is also useful.

The aqueous medium can be soft, brackish, or brine water. Preferably, the water is soft but it can contain small amounts of salts.

Useful surfactants include the various nonionic, cationic, and anionic surfactants. Examples of surfactants can be found in US. 3,254,714 to Gogarty et al. Preferably, the surfactant is a petroleum sulfonate, also known as alkaryl sulfonates or alkaryl naphthenic sulfonates. The sulfonate can contain less than 60 or up to 100% active sulfonate. Examples of preferred surfactants are the sodium and ammonium petroleum sulfonates having an average equivalent weight within the range of from about 360 to about 520, and more preferably from about 400 to about 470. The surfactant can be a mixture of low and high average equivalent weight sulfonates or of a mixture of different surfactants.

Examples of useful cosurfactants include alcohols, amino compounds, esters, aldehydes and ketones containing from 1 up to about 20 or more carbon atoms and more preferably from about 3 to about 16 carbon atoms. The cosurfactant is preferably an alcohol, e.g. isopropanol, nand isobutanol, the amyl alcohols such as n-amyl alcohol, 1- and Z-hexanol, 1- and 2-octanol, decyl alcohols, alkaryl alcohols such as p-nonyl phenol and alcoholic liquors such as fusel oil. Particularly useful alcohols include the primary butanols, primary pentanols and secondary hexanols. Concentrations of from about 0.1% to more than about 5% by volume are preferred and more preferably from about 0.2% to about 3%. Mixtures of two or more cosurfactants are also useful.

Electrolytes useful within the micellar dispersions include inorganic bases, inorganic acids, inorganic salts, organic bases, organic acids, and organic salts. These electrolytes include those being strongly or weakly ionized. Preferably, the electrolytes are inorganic bases, inorganic acids, and inorganic salts, examples include sodium hydroxide, sodium chloride, sodium sulfate, hydrochloric acid, sulfuric acid, sodium nitrate, ammonium chloride, ammonium hydroxide, and potassium chloride. Examples of other useful electrolytes can be found in US. Pat. No. 3,330,344.

In the graph depicted in the figure, a conductivity example is presented to specifically illustrate the working embodiments of this invention. This example is not intended to limit the invention, but, it is intended that all equivalents obvious to those skilled in the art be interpreted within the scope of the invention as defined in the specification and appended claims. The data for this particular conductivity vs. micellar dispersion concentration graph was produced by systematically diluting with water a solution initially comprised of 84% hydrocarbon (Crude Column Overhead) and approximately 16% surfactant (Marathon Detroit Sulfonate 57D-166 comprised of 2,.6% salt, 13.2% water, 7.2% isopropyl alcohol, 60.8% ammonium sulphonate, and 16.2% vehicle oil and having an equivalent weight of 457).

The addition of even a 1 millimeter layer of the micellar dispersion to the soil surrounding the metallic object should impart a considerably lower conductivity (about lower) to this soil. The upper limit of application will be established by the economics of saturating increasingly larger soil volume surrounding the metallic object to be protected. Since the nature of the soil surrounding the metallic object including water content, pH, local precipitation and drainage conditions determine the resistivity and hence the corrosivity of the soil, it may be necessary to vary the composition of the micellar solution to meet local conditions. In those areas where the leaching effect of rainfall may be great it may be necessary to raise the viscosity of the micellar dispersion. This can be carried to the point where the micellar dispersion becomes a gelatinous substance. The viscosity can be raised by varying the basic ingredients of the micellar dispersion. For instance, the alcohol content could be lowered or a hydrocarbon having a higher viscosity could be employed,

etc. It is also recognized that leaching efiects due to capillary action and evaporation can be minimized by using hydrocarbons with high boiling points in the preparation of the micellar dispersion.

The micellar dispersions used in this invention can be introduced into the soil in a variety of ways, such as mixing with back fill material by the use of known mechanical mixers or by hand. The solution may also be applied to the surface above the metallic object and allowed to soak in, or ditches may be dug or holes drilled and the solution introduced into these. Perhaps the most convenient method of application is by means of injection pipes. The main advantage of using such pipes is that pressure can be applied to the solutions and the solutions forced into the ground to the desired distance and extent required by local conditions. The extent of penetration can be determined by measurement of soil conduc tivity at a series of points. The method of applications may be controlled by local soil conditions as well as economic factors. Ideally the surroundings into which the metallic objects are to be placed should contain a highly porous material such as sand or gravel so as to allow the micellar solution to impregnate the void space surrounding the metallic object.

EXAMPLE 1 A micellar dispersion containing approximately 40% crude oil, 50% Water, 8% petroleum sulfonate surfactant, and 2% primary amylalcohol cosurfactant, is mixed with the soil used to back fill the six inches immediately adjacent to a '24" diameter buried petroleum pipeline. Approximately l4 gallons of the micellar dispersion is mixed with the soil used to back fill one linear foot of the pipeline. The pipeline is thus protected from stray electric currents by the high resistance micellar dispersion-containing soil which is interposed between the pipeline and the surrounding soil which has relatively high electrical conductivity due to its nautral moisture content.

What is claimed is:

1. A process for protecting metallic objects buried in the soil from corrosion comprising introduction of high resistance micellar dispersions having a continuous phase and at least one discontinuous phase, at least one of said phases containing water and at least another of said phases containing hydrocarbon into the soil surrounding the metallic objects so as to displace water from the surrounding soil and thereby insulate said metallic objects from corrosion-causing electrochemical currents.

2. The process of claim 1 in which the micellar dispersions contain up to Water.

3. The process of claim 1 in which at least a 1 millimeter layer of the micellar dispersions impregnated soil is in contact with the metallic object to be protected.

4. The process of claim 1 in which the dispersions are oil external micellar dispersions.

5. The process of claim 4, wherein the micellar dispersions are comprised of surfactant, aqueous medium, hydrocarbon, and at least one ingredient selected from the group consisting of cosurfactants and electrolytes.

6. The process of claim 5 wherein the surfactant is a petroleum sulfonate.

7. A process for supplementing the corrosion inhibiting capabilities of cathodic protection systems or sacrificial anode protection systems comprising injecting into the soil adjacent the elements of said systems a micellar dispersion of loW conductivity so as to displace water from surrounding soil and increase the electrical resistivity of the soil, said micellar dispersion having one continuous phase and at least one discontinuous phase, at least one of said phases containing hydrocarbon and at least another of said phases containing water.

8. The process of claim 7 in which at least a l millimeter layer of the micellar dispersion impregnated soil is in contact with the metallic object to be protected.

9. The process of claim 7 in which is used an oil external micellar dispersion.

10. The process of claim 9 in which the oil external 2,979,377 4/1961 Hitzman 21-25 micellar dispersion contains up to 70% water. 3,192,720 7/ 1965 Schaschl et al. 61-35 11. The process of claim 9 wherein the micellar 3,484,349 12/1969 Vrable 204-147 dispersion is comprised of surfactant, aqueous medium, 3,016,713 1/1962 Deming 61-35 X hydrocarbon, and at least one additional ingredient 5 3,520,141 7/ 1970 Routson 61-35 X selected from the group consisting of cosurfactants and 2,558,159 6/1951 Sanick 174-6 electrolytes.

12. The process of claim 11 wherein the surfactant is MORRIS WOLK, Primary EXaminel Petroleum sulfonate- 10 D. G. MILLMAN, Assistant Examiner References Cited CL UNITED STATES PATENTS 3,168,455 2/1965 Shapiro 204-147 2,955,018 10/1960 Schaschl et a1. 21-2.5 

